I really like the draining life from the area around you idea. Feel like it could also work as a generalized necromancer ability, maybe to self-heal or supplement eating/drinking/blood/souls across races. Love the thought generally of the character in one way or another visually spreading its influence behind where it walks, reminds me of the game Black & White in presentation. Gameplay/fun issues could probably be mitigated with clever placement of life in various forms crammed into nooks and crannies to incentivize exploration :) For instance, I haven't explored the Capital fully yet, but it feels like the kind of place that would have catacombs/sewers/dungeon systems with some emergency life essence tucked away for the taking. If you end up going the route with multiple z-levels and flying, perhaps migrating birds could fill some gaps in sparsely populating a desolated area.
With the ability morphing, yeah I was talking very long term :P Intrigued about the modding support, my skill level is maybe about to where I could reverse engineer my way through some of the jsons through some trial and error to add something if I had an idea I was really excited about, but I'm so visually focused an editor would probably be a huge boon to time and effort if I did take anything up.